2 Sample Preparation
Table 2 synthesizes the recent analytical techniques in terms of extraction,
purification, and instrumental analysis showing recoveries and method limit of
detection (MLOD) for determination of pyrethroids in environmental and food
matrices.
2.1 Extraction from Water Sample
Pyrethroid concentrations in water are generally low, as they are preferentially
sorbed to soil or sediment, due to their hydrophobic character. Thus, analytical
methods for determination of pyrethroids in water should include extraction and
pre-concentration to reach the required limits of detection. Liquid-liquid extraction
(LLE) is the most common extraction technique for water samples. Its main drawbacks are the high solvent consumption and the long analysis time. For this reason,
alternative extraction methods in which solvent consumption and time of analysis
are reduced were introduced. Among these are solid-phase extraction (SPE), solidphase microextraction (SPME), and stir bar sorptive extraction (SBSE). Moreover,
recently, liquid-liquid microextraction (LLME) and LLME based on solidification of
floating organic droplet (LLME-SFO) have been developed. LLE of pyrethroids
from water uses nonpolar solvents such as dichloromethane [15] and hexane
[16]. After extraction, the sample is dried and redissolved in a small volume of
organic solvent ready to be injected into GC for analysis. Pyrethroid recoveries by
LLE were in the range 75–115% for unfiltered river samples with method limit of
detection (MLOD) of 1–3 ng/L [15] and 94–105% for aqueous solution [16]. Dispersive liquid-liquid microextraction (DLLME) assisted by ultrasound was developed by Yan et al. as a method for the pre-concentration and determination of six
pyrethroids in river water samples [17]. Tetrachloromethane was used as waterimmiscible extractant, and acetone was used as water-miscible dispersive solvent.
Ultrasonic treatment was performed to make the analytes fully extracted into the fine
droplets. The phase separation was performed by a rapid centrifugation. Recoveries
were ranging between 86 and 109%. MLODs were 0.1–0.30 μg/L [17]. A novel
LLME based on solidification of floating organic droplet (LLME-SFO) has been
recently developed by Khalili-Zanjani et al. which was based on the extraction of the
analytes by microliter volume of the extraction solvent (floated on the surface of the
aqueous sample) from the aqueous sample matrix [53]. In this method, small volume
of an organic solvent with a melting point near room temperature (in the range of
10–30
C, such as undecanol and 1-dedecanol) is floated on the surface of aqueous
solution. Transferring the sample in an ice bath, the organic solvent microdrop is
solidified and ready to be transferred into a conical vial where it melts immediately at
room temperature and thus is ready to be injected into a GC for analysis. The
advantages of the method are simplicity of operation, small amount of solvent
24
M. L. Feo
Table 2 synthesizes the recent analytical techniques in terms of extraction,
purification, and instrumental analysis showing recoveries and method limit of
detection (MLOD) for determination of pyrethroids in environmental and food
matrices.
2.1 Extraction from Water Sample
Pyrethroid concentrations in water are generally low, as they are preferentially
sorbed to soil or sediment, due to their hydrophobic character. Thus, analytical
methods for determination of pyrethroids in water should include extraction and
pre-concentration to reach the required limits of detection. Liquid-liquid extraction
(LLE) is the most common extraction technique for water samples. Its main drawbacks are the high solvent consumption and the long analysis time. For this reason,
alternative extraction methods in which solvent consumption and time of analysis
are reduced were introduced. Among these are solid-phase extraction (SPE), solidphase microextraction (SPME), and stir bar sorptive extraction (SBSE). Moreover,
recently, liquid-liquid microextraction (LLME) and LLME based on solidification of
floating organic droplet (LLME-SFO) have been developed. LLE of pyrethroids
from water uses nonpolar solvents such as dichloromethane [15] and hexane
[16]. After extraction, the sample is dried and redissolved in a small volume of
organic solvent ready to be injected into GC for analysis. Pyrethroid recoveries by
LLE were in the range 75–115% for unfiltered river samples with method limit of
detection (MLOD) of 1–3 ng/L [15] and 94–105% for aqueous solution [16]. Dispersive liquid-liquid microextraction (DLLME) assisted by ultrasound was developed by Yan et al. as a method for the pre-concentration and determination of six
pyrethroids in river water samples [17]. Tetrachloromethane was used as waterimmiscible extractant, and acetone was used as water-miscible dispersive solvent.
Ultrasonic treatment was performed to make the analytes fully extracted into the fine
droplets. The phase separation was performed by a rapid centrifugation. Recoveries
were ranging between 86 and 109%. MLODs were 0.1–0.30 μg/L [17]. A novel
LLME based on solidification of floating organic droplet (LLME-SFO) has been
recently developed by Khalili-Zanjani et al. which was based on the extraction of the
analytes by microliter volume of the extraction solvent (floated on the surface of the
aqueous sample) from the aqueous sample matrix [53]. In this method, small volume
of an organic solvent with a melting point near room temperature (in the range of
10–30
C, such as undecanol and 1-dedecanol) is floated on the surface of aqueous
solution. Transferring the sample in an ice bath, the organic solvent microdrop is
solidified and ready to be transferred into a conical vial where it melts immediately at
room temperature and thus is ready to be injected into a GC for analysis. The
advantages of the method are simplicity of operation, small amount of solvent
24
M. L. Feo